1. Filed of the Invention
The invention relates to a fuel injector having an orifice region in which an orifice passage extends along an injector axis. The fuel injector is suitable in particular for liquid fuel.
2. Related Art
Described in DE 32 35 080 A1 is a spill-type injector in which two liquid feeds opposed to one another open tangentially into a circular-cylindrical swirl space. An injection passage on the one hand and, in opposition thereto, a return bore on the other hand are connected to the swirl space. The spill-type injector is suitable in particular for the atomization of liquid fuel in gas-turbine combustion chambers. Atomization is achieved by virtue of the fact that fuel flows tangentially into the swirl chamber and is combined to form a main flow, in the course of which a swirl is imparted to the main flow by circular guidance in the swirl chamber, this swirl being maintained in the injection passage. As a result, the fuel jet fans out conically during the discharge of the fuel from the injection passage. On the other hand, fuel is returned via the return bore. While maintaining a constant fuel inflow to the spill-type injector, the quantity of injected fuel is controlled by the quantity of returned fuel being set.
In the article xe2x80x9cAktive Dxc3xa4mpfung selsterregter Brennkammerschwingungen (AIC) bei Druckzersxc3xa4uberbren-nern durch Modulation der flxc3xcssigen Brennstoffzufuhrxe2x80x9d [Active damping of self-excited combustion-chamber vibrations (AIC) in the case of pressure-atomizer burners by modulation of the liquid fuel feed] by J. Hermann, D. Vortmeyer and S. Gleis, VDI-Berichte No. 1090, 1993, it is described how a combustion vibration is generated in the combustion chamber of a gas turbine or a boiler and how it can be actively damped. This is because the abovementioned self-excited combustion vibration behavior, which is also referred to as combustion instability, can occur during combustion in the combustion chamber. Such a combustion vibration is generated by the interaction between a fluctuating heat release during combustion and the acoustics of the combustion chamber. A combustion vibration is often accompanied by a high emission of noise and mechanical loading of the combustion chamber, which may lead to destruction of components.
DE-A 20 33 118 shows a gas burner for a gas-fired smelting furnace. In order to create a high flame temperature, the gas burner has an injector which is in the form of a gap and converges in the region of the orifice. A high heat concentration is thereby ensured.
The object of the invention is to specify a fuel injector by means of which a combustion vibration is at least reduced.
According to the invention, this object is achieved by a fuel injector having an orifice region in which an orifice passage extends along an injector axis and ends at an orifice edge in a non-convergent manner, the orifice edge being rotationally asymmetrical about the injector axis.
Fuel is directed in the fuel injector through the orifice region in the orifice passage. The orifice passage is designed to be non-convergent in the orifice region, that is to say it does not narrow, so that no pressure loss occurs. The fuel discharges from the orifice passage at the orifice edge into the exterior space. In the process, the jet widens, i.e. a divergent, fanned-out fuel jet is obtained. Owing to the fact that the orifice edge is rotatationally asymmetrical about the injector axis, the divergent fuel jet is also rotationally asymmetrical. A distorted fuel cone is thus obtained, and this distorted fuel cone has a different extent perpendicular to the jet direction at least in two spatial directions. The spatial zone in which the combustion takes place is distorted in a corresponding manner. This distortion of the combustion zone influences the generation of a combustion vibration. The zone of the combustion is displaced and spread in such a way that the acoustic system of burner and burner surroundings is detuned. The fuel injector and thus the discharging fuel cone are oriented in such a way that a reduction in the combustion vibrations right up to complete suppression of the combustion vibrations is obtained.
The orifice edge is preferably asymmetrical about the injector axis. This means that the orifice edge must undergo a complete revolution about the injector axis in order to coincide again with its original position.
In one embodiment the orifice edge preferably has twofold symmetry. In this case, the orifice edge is more preferably an ellipse or a rectangle, preferably with rounded-off corners.
The twofold symmetry means that the orifice edge must undergo half a revolution, i.e. 180xc2x0, in order to coincide with its original position.
In a second embodiment the orifice edge preferably corresponds to a contour which is formed by a rectangle and a circle, the circle lying with its center on the centroid of the rectangle and extending beyond the narrow side of the rectangle, and the contour enclosing the outer edge of the rectangle and the circle.
In a third embodiment the orifice edge preferably corresponds to a contour which is formed by two rectangles which are perpendicular to one another and have a common centroid, the contour enclosing the outer edge of both rectangles.
In a fourth embodiment the orifice passage preferably has a passage wall, each point of the passage wall being at a distance from the injector axis and having an axial position along the injector axis, the distance from the axis for at least two points on the passage wall which have the same axial position being different. The distance from the axis for points on the passage wall having the same axial position more preferably changes continuously in a circumferential direction about the injector axis. The orifice passage is thus rotationally asymmetrical about the injector axis. The fuel is thus already directed for a short distance in the orifice region in a rotationally asymmetrical flow. A rotationally asymmetrical form is thus imposed on the fuel flow and leads in an especially efficient manner to the formation of a rotationally asymmetrical, distorted fuel cone during the discharge of the fuel from the fuel injector. In a fifth embodiment the orifice passage preferably widens toward the orifice edge.
In still another embodiment the orifice edge preferably has a notch. Due to such a notch, fuel is deflected to a greater extent in the direction of the notch than in the other directions of the orifice edge during the discharge from the fuel injector. Such a notch in turn therefore achieves the effect that fuel is not deflected to an equally pronounced degree in all spatial directions. A distorted fuel cone is likewise formed.
The fuel injector of this invention is preferred for liquid fuel, in particular crude oil. The fuel injector is preferably used in a burner for a gas turbine, in particular for a stationary gas turbine.